The process whereby integral membrane proteins are synthesized and inserted into biological membranes will be studied, using the major capsid protein of coliphage M13 as a model. This protein is an integral protein of the host cell plasma membrane at each stage of virus infection. It is made as a soluble precursor, "procoat", which we have isolated in radiochemically-pure form. We have also purified a protease which converts the precursor "procoat" to mature "coat protein"; this protease is called leader peptidase. We will study: 1. The role of electrical potential in membrane assembly. 2. The basis of leader peptidase specificity. 3. The effects of mutation in leader peptidase. 4. The role of lipid fluidity on protein insertion into membranes.